1. Interviews are individual and are open-file. You will be interviewed by 1 faculty member and 1 (usu. 3rd yr) student. It lasts 30 mintues, w/o a set question list (so come prepared with q's of your own).
2. Interview Day was mid-Feb this year; I imagine it will be around the same time next year.
3. Early Admissions is based almost entirely on grades and OAT scores. In general, you can't go wrong with a high GPA and OAT score; but, like any other program, sometimes they really like a particular candidate with other experiences, so grades are no guarantee for acceptance.
* Oh, I thought of a good reason for turning in your app early: if you have high grades/OAT, you can be considered for early admissions! (not my case, so I can't really give you a pulse on that process)
Als, check out Rosanna's UCBSO FAQ thread; it's got some very useful stuff there.
-p.dot